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Biomedical subjects

J Pauly

Publications and source records attributed to J Pauly.

At least 19 recordsLinked to original sources
PubMed1999

1999 Gary J. Becker Young Investigator Award. MR-guided transjugular portosystemic shunt placement in a swine model.

PURPOSE: To evaluate the performance of portal venous puncture with use of magnetic resonance (MR) guidance, and to place a transjugular intrahepatic portosystemic shunt (TIPS) in a swine model. MATERIALS AND METHODS: A study of 12 swine was performed to evaluate the ability of interventional MR imaging to guide portal vein puncture and TIPS placement. Six swine had catheters placed in the right hepatic vein under C-arm fluoroscopy. A nitinol guide wire was left in the vein and the animals were then moved into an open configuration MR imaging unit. A TIPS needle set was used to puncture the portal vein using MR fluoroscopy. The animals were transferred to the C-arm, and venography confirmed portal vein puncture. A follow-up study was performed in six additional swine to place a TIPS using only MR imaging guidance. MR tracking was used to advance a catheter from the right atrium into the inferior vena cava. Puncture of the portal vein was performed and a nitinol stent was placed, bridging the hepatic parenchyma. MR venogram confirmed placement. RESULTS: Successful portal vein puncture was achieved in all animals. The number of punctures required decreased from 12 in the first animal to a single puncture in the last eight swine. A stent was successfully placed across the hepatic tract in all six swine. CONCLUSIONS: Real-time MR imaging proved to be a feasible method to guide portal vein puncture and TIPS placement in pigs.

Animals↗
PubMed1997

RARE spiral T2-weighted imaging.

Spiral imaging has a number of advantages for fast imaging, including an efficient use of gradient hardware. However, inhomogeneity -induced blurring is proportional to the data acquisition duration. In this paper, we combine spiral data acquisition with a RARE echo train. This allows a long data acquisition interval per excitation, while limiting the effects of inhomogeneity. Long spiral k-space trajectories are partitioned into smaller, annular ring trajectories. Each of these annular rings is acquired during echoes of a RARE echo train. The RARE refocusing RF pulses periodically refocus off-resonant spins while building a long data acquisition. We describe both T2-weighted single excitation and interleaved RARE spiral sequences. A typical sequence acquires a complete data set in three excitations (32 cm FOV, 192 x 192 matrix). At a TR = 2000 ms, we can average two acquisitions in an easy breath-hold interval. A multifrequency reconstruction algorithm minimizes the effects of any off-resonant spins. Though this algorithm needs a field map, we demonstrate how signal averaging can provide the necessary phase data while increasing SNR. The field map creation causes no scan time penalty and essentially no loss in SNR efficiency. Multiple slice, 14-s breath-hold scans acquired on a conventional gradient system demonstrate the performance.

Abdomen↗
PubMed1997

Background suppression with multiple inversion recovery nulling: applications to projective angiography.

We have developed a technique to accurately null the longitudinal magnetization (Mz) of background material. This suppression involves first saturating the longitudinal magnetization (Mz) of a region, and then applying several nonselective inversions. The inversions are timed relative to the saturation such that Mz is nulled across a broad range of T1 at a predetermined time after the initial saturation. B1 and B0 inhomogeneity, which could lead to inaccurate suppression, are dealt with by the combination of a multiple tip saturation sequence and four adiabatic inversion pulses. The suppression sequence can be used to form projective angiograms by selectively tagging the imaging region with the saturation pulse. After the inversions are played out, a projection taken through the tag region when Mz is nulled will only contain signal from blood that has flown into the region after the saturation. Since only two dimensions are acquired, the technique can acquire gated projection angiograms in reasonable scan times. Representative inflow MIR angiograms of the carotid arteries and renal arteries show excellent background suppression.

Carotid Arteries↗
PubMed1997

Consistent fat suppression with compensated spectral-spatial pulses.

Reliable fat suppression is especially important with fast imaging techniques such as echo-planar (EPI), spiral, and fast spin-echo (FSE) T2-weighted imaging. Spectral-spatial excitation has a number of advantages over spectrally selective presaturation techniques, including better resilience to B0 and B1 inhomogeneity. In this paper, a FSE sequence using a spectral-spatial excitation pulse for superior fat suppression is presented. Previous problems maintaining the CPMG condition are solved using simple methods to accurately program radio-frequency (RF) phase. Next an analysis shows how B0 eddy currents can reduce fat suppression effectiveness for spectral-spatial pulses designed for conventional gradient systems. Three methods to compensate for the degradation are provided. Both the causes of the degradation and the compensation techniques apply equally to gradient-recalled applications using these pulses. These problems do not apply to pulses designed for high-speed gradient systems. The spectral-spatial FSE sequence delivers clinically lower fat signal with better uniformity than spectrally selective pre-saturation techniques.

Adipose Tissue↗
PubMed1997

Isotropic diffusion-weighted and spiral-navigated interleaved EPI for routine imaging of acute stroke.

An interleaved echo-planar imaging (EPI) technique is presented for the rapid acquisition of isotropic diffusion-weighted images of stroke patients. Sixteen isotropic diffusion-weighted images at three b values are acquired in less than 3 min. A spiral navigator echo is used to measure the constant and linear phase shifts across the head in both the x and y directions which result from motion during the isotropic diffusion- sensitizing gradients. The measured k-space errors are corrected during a gridding reconstruction. The gridding kernel has a constant width in kx and a variable width in ky which eliminates variable data-density ghosts. The resulting isotropic diffusion-weighted images have excellent lesion-to-normal brain contrast, very good spatial resolution, and little sensitivity to susceptibility effects in the base of the brain. Examples of diffusion-weighted images and ADC maps from several stroke patients are shown.

Acute Disease↗
PubMed1994

Short TE phosphorus spectroscopy using a spin-echo pulse.

In vivo phosphorus spectroscopy requires very short acquisition delays in order to capture the signal from components with short transverse relaxation times (T2). The echo time typical of standard slice selective spin-echo pulses are too long for this application, so hard pulse, free induction decay (FID) acquisitions have frequently been used instead. With FID, however, there is an interval between the time of coherence and data acquisition (acquisition delay), with resulting baseline distortions. In this paper we describe the design of a new short TE, slice-selective, composite spin-echo pulse with echo times as short as 2.5 ms. With a long TR, fully relaxed, multislice spectra can be collected. This technique will be useful for assessing in vivo, changes in brain phospholipid activity associated with psychiatric and neurological diseases.

Brain↗
PubMed1993

Echo-planar spin-echo and inversion pulses.

The echo-planar k-space trajectory can be used as the basis for any two-dimensional selective pulse. The main application is spectral-spatial pulses, which must be based on the echo-planar trajectory. In this paper we show how echo-planar spin-echo (EPSE) pulses may be designed.

Body Water↗
PubMed1993

Magnetic resonance imaging of lung parenchyma.

Imaging of the lungs presents a unique challenge for MR technology. Signal from lung parenchyma is limited by low proton density, the effects of motion and susceptibility, and a multiexponential T2 relaxation time. We have illustrated the use of spin echo and projection reconstruction MR sequences in imaging lung parenchyma, and the use of a GRE sequence in imaging the pulmonary vascular tree.

Humans↗
PubMed1992

Effects of RF amplifier distortion on selective excitation and their correction by prewarping.

In a magnetic resonance imaging system, an RF power amplifier is employed to boost an RF pulse to sufficient strength to excite the nuclear spins in a subject. The nonideal behavior of this amplifier distorts a selective-excitation pulse, and this distortion in turn degrades the slice profile. We have found two types of nonideal behavior particularly troublesome: nonlinearity and incidental phase modulation. One of their effects is the introduction of an unwanted "skirt" in the out-of-slice region of a slice profile. We present an effective method of correction in which a selective-excitation pulse is prewarped to compensate for the distortion.

Algorithms↗
PubMed1992

Two-dimensional selective adiabatic pulses.

Using the technique of separable k-space excitation, we have designed a two-dimensional selective adiabatic pulse that inverts magnetization from a square region in the xy plane with insensitivity to RF variations. We also have designed a two-dimensional adiabatic pulse that inverts selectively in frequency and in one spatial dimension. The pulses should be useful for both MR imaging and spectroscopy. We present experimental results to demonstrate that the two-dimensional adiabatic pulses are feasible on commercial MR imaging systems.

Humans↗
PubMed1991

Spectroscopic imaging with multidimensional pulses for excitation: SIMPLE.

Proton spectroscopy and spectroscopic imaging in the human brain require the elimination of both water and lipid signals. Strong lipid signals from subcutaneous fat are usually eliminated by confining the excited volume to lie wholly within the skull. Water suppression, however, can be difficult due to both B0 and RF inhomogeneities, which are particularly troublesome in imaging experiments where a relatively large region-of-interest (ROI) is typical. In this paper, we discuss the use of multidimensional selective-excitation pulses (e.g., pulses that are simultaneously selective along two axes) to both define the ROI and provide the necessary water suppression. Pulse sequences providing three-dimensional localization along with water suppression that is insensitive to a range of B0 and RF inhomogeneities are described. Spectra and spectroscopic images (voxel volume = 3.4 cc. acquisition time = 38 min) of various 1H metabolites from a patient with an astrocytoma show clear differences between normal and cancerous tissues and demonstrate the ability of these techniques to be used in vivo.

Astrocytoma↗
PubMed1983

Studies of cultured human T lymphocytes. II. Initiation of paired T- and B-cell lines from healthy donors.

We report the sustained cultivation of both B- and T-lymphoblastoid cell lines from randomly selected healthy donors, and the results of studies defining the frequency with which these cell lines can be established. B-cell lines were initiated using the Epstein-Barr virus. Of 52 attempts, 40 B-cell lines (77% success) were obtained from 24 different donors. T-cell lines were started and propagated in long-term (greater than 100 days) cultures using the T-cell growth factor interleukin-2 (IL-2). Of 55 attempts, 54 (98%) were successful in initiating IL-2-dependent T-cell lines, and these were derived from 28 healthy adults. Likewise, of 45 attempts, 32 (71%) were successful in producing paired lines in which both the B-cell line and T-cell line were cultivated from a single blood collection (N = 22 donors). Phenotypic profiles of these lines were defined using multiple marker assays, including rosette formation, surface immunoglobulins, cytochemistry, karyotype, as well as xenoantisera and monoclonal antibodies defining different membrane antigens. This work demonstrates the feasibility of propagating paired human B and T lymphoblastoid lines suitable for many comparative immunobiological studies.

Adolescent↗
PubMed1976

Adenosine-aminohydrolase activity in the erythrocytes, lymphocytes, and plasma of healthy subjects and kidney transplant recipients.

Adenosine-aminohydrolase activity in the red blood cells and lymphocytes of transplant patients were assayed by continuous flow analysis. This enzyme, which has been implicated in the ability of lymphocytes to mount an immune response, was evaluated in renal allografted patients immunosuppressed by azothiprine and methylprednisone. Red cell adenosine-aminohydrolase activity was depressed in all patients when compared to nontreated health controls. Adenosine aminohydrolase activity was raised in the lymphocytes of the renal allografted patients. Renal transplant patients' in vitro lymphocyte reactivity to antigens, mitogens, or skin testing to specific antigens, confirmed the depressive effects of immunosuppression observed in vivo. We conclude from these studies that red cell adenosine-aminohydrolase activity may be a more sensitive index of the state of immunoresponsiveness than the corresponding enzyme activity in the lymphocyte.

Adenosine Deaminase↗